Patent GB-1222342-A (GB)
Title: A device for detecting the position of a probe
IPC: G06F3/046
Filed: 1969-05-06
Abstract: 1,222,342. Inductive signalling. INTERNATIONAL BUSINESS MACHINES CORP. 6 May, 1969 [6 June, 1968 (2)], No. 23047/69. Heading H4U. [Also in Division G4] In a device for detecting the position of a probe on a surface, e.g. to enable an operator to identify a particular part of an image on a cathode-ray tube, the probe radiates an electromagnetic field and co-operates with two arrays of spaced conductors on the surface, the first array being arranged so as to intersect the second array, means being provided to sense the outputs on the conductors to determine the position of the probe. In one arrangement, Fig. 1, parallel vertical conductors V1 to V9 and parallel horizontal conductors H1 to H7 are supported on a viewing screen S, the conductors V and H being insulated from each other and one end of the conductors being connected via a conductor R to ground. Conductors V1, V2 are connected to the inputs of a differential sense amplifier SAX1 providing an output on conductor X1 when correctly energized, conductors V2, V3 are connected to the inputs of a differential sense amplifier SAX2 and so on. Conductors H1 to H7 are connected similarly to differential sense amplifiers SAY1 to SAY6 thus providing fortyeight response points. The arrangement is such that if, for example, the probe P is at the position shown, currents will be induced in the conductors but only the adjacent conductors H4, H5 and V4, V5 will carry currents of opposite phase so that amplifiers SAY4 and SAX4 will provide outputs Y4 and X4 respectively. In a modification, Figs. 3A, 3B (not shown), which reduces the number of amplifiers required, the grid of conductors is separated into two areas forming two groups, the corresponding first, second, third &c. vertical conductors of each group being connected together to first, second, third &c. amplifiers. An additional loop co-operates with the conductors of one of the groups and with a separate amplifier to provide a signal distinguishing between the two groups. The horizontal conductors may be similarly arranged so that the grid is divided into four areas. The probe P, Fig. 7 (not shown), includes a spring-loaded switch which switches on an R.F. oscillator when the probe is applied to the screen. Alternative arrangement, Fig. 4.-Spaced elongated vertical loops VL1 to VL5 are supported on the screen S and horizontal elongated loops HL1 to HL8 are similarly arranged on the screen, the loops being insulated from each other. The vertical loops are connected to sense amplifiers SAX1 to SAX5 respectively and the horizontal loops to sense amplifiers SAY1 to SAY8, the amplifiers providing an output whenever a radiating probe is bracketed by a conductive loop. Thus, when the probe P is located as shown, outputs X4, Y5 are provided by amplifiers SAX4, SAYS respectively, but at point A no output is provided and at point B only one amplifier, SAX3, provides an output. The sense amplifiers, Fig. 5 (not shown), have an input circuit tuned to the frequency radiated by the probe. Since the loops are elongated, stray currents induced in the parallel portions are not additive and produce no effect on the amplifier. In a modification, Fig. 6 (not shown), certain of the loops are tuned to a supervisory frequency and the remaining loops are tuned to the operator frequency, the supervisor's probe being provided with two oscillators supplying both frequencies and the operator's probe supplying only the operator frequency. Alternatively, the loops may be untuned, the supervisor and operator probes each radiating a single unique frequency. Selected amplifiers are tuned to both frequencies and the remainder to the supervisory frequency only.